Generally, a semiconductor gas sensor can detect a gas using an oxide semiconductor material having a variable resistance when contacting a particular kind of gas. The semiconductor gas sensor can be manufactured through a semiconductor manufacturing process. The semiconductor gas sensor has advantages of having relatively small size, low manufacturing costs, a high sensitivity and a high response speed.
The semiconductor gas sensor includes a substrate, a heating electrode, a sensing electrode formed over the heating electrode, a detection layer to cover the sensing electrode, and a plurality of insulation layers stacked on the substrate. The detection layer is a member to substantially detect gas and is formed using an oxide semiconductor material. While the detection layer is exposed to gas, gas can be adsorbed to a surface of the detection layer to have a value of the resistance varied to detect whether gas exists. In particular, the semiconductor gas sensor may be required to maintain a temperature of the detection layer over 300° C. in order to secure a gas detection, thus that it may be necessary for the heating electrode formed under the detection layer to generate heat to be transmitted to the detection layer for an efficient detection of the detection layer.
However, the semiconductor gas sensor may be damaged because the durability of the semiconductor gas sensor may be deteriorated due to heat. In order to improve the thermal durability of the semiconductor gas sensor, the semiconductor gas sensor may have a cavity formed under the heating electrode to dissipate heat from the heating electrode. The cavity may be formed by partially removing the substrate and a plurality of insulation layers stacked on the cavity may cover the cavity to form a membrane structure.
A portion covering the cavity may not be stably supported by the substrate such that a membrane structure formed over the cavity may sag. Thus, a sag phenomenon occurred to the membrane may be caused by a thermal stress or an intrinsic stress which the membrane has.
In particular, the heating electrode may be required to keep a resistance uniform in order to transmit heat to the sensing electrode stably. When the membrane sags, the resistance of the heating electrode disposed in the membrane may vary, and thus it may be difficult for the heating electrode to provide heat for the sensing electrode stably. Further, due to the sag of the membrane, a heated area of the sensing electrode may deform such that a temperature distribution of the sensing area is non-uniform.